This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objective: To evaluate the impact of AIDS virus evolution on the design of vaccines, we will determine whether mutations that facilitate AIDS virus escape from CD8+ T-cell responses also affect viral fitness in vitro and in vivo. We are also attempting to determine the major factors that contribute to elite control of AIDS virus replication. We have recently developed an animal model of elite control in Mamu-B*08+ Indian rhesus macaques. Remarkably, 50% of Mamu-B*08+ Indian rhesus macaques control replication of SIV, and Mamu-B*08 and HLA-B*27 bind similar peptides. Thus, these Mamu-B*08+ macaques are ideal for modeling human ECs. Understanding why ECs suppress viral replication should facilitate the development of an effective HIV vaccine. Elite controllers of HIV and SIV are studied with the goal of understanding immunological mechanisms underlying successful control of immunodeficiency virus replication. Elite control is associated with particular MHC class I alleles, implicating CD8+ T cells as mediators of control. Since in vivo CD8+ cell depletion in two Mamu-B*08+ EC rhesus macaques results in an immediate increase in viral replication, CD8+ lymphocytes are likely important for control in these ECs. Interestingly, SIVmac239[unreadable]nef-vaccinated Mamu-B*08+ macaques exhibit almost complete control of a heterologous SIVsmE660 challenge. Additionally, HLA-B*27 and Mamu-B*08 bind the same peptides requiring an arginine at position 2, and antigen-specific Mamu-B*08-restricted CD8+ T cell responses dominate the acute phase in ECs. These results implicate MHC class I-bound peptide-specific memory CD8+ T lymphocytes in control of viral replication in Mamu-B*08+ rhesus macaques. Our initial experiment using an 8X mutant virus containing viral escape mutations in all of the B*08-restricted immunodominant epitopes, demonstrated that CD8 T cell responses are important in B*08-associated elite control. At week 14 post-infection the geometric mean viral load for ten Mamu-B*08+ animals infected with SIVmac239 was 5,500 vRNA copy Eq/ml plasma, whereas the group of ten animals infected with 8X-SIVmac239 had a geometric mean viral load of 101,000 vRNA copy Eq/ml plasma. In spite of this significant difference, two of the ten 8X animals became ECs. In addition, the 8X-infected animals made substantially more frequent responses to the subdominant B*08-restricted epitopes that were not mutated in the 8X construct. Some 8X animals also responded, albeit much less frequently than the wild-type infected animals, to four of the eight mutated epitopes. We have therefore created a new mutant virus construct, termed 12X, that both introduces escape mutations into the previously non-mutated subdominant epitopes and re-introduces "better" escape mutations into the epitopes that exhibited breakthrough in the 8X experiment. We are presently in the process of making and testing this virus in vitro. It is then our intention to introduce the 12X virus into 10 non-B*08 animals to completely evaluate the in vivo fitness of the new construct before infecting another group of B*08+ macaques. We have also initiated a new direction as a part of this project systematically investigating the outcomes of various CD8 T cell escape mutations in viruses transmitted to individuals that do not harbor the restricting MHC allele for the particular mutation. Recent evidence from human cohort studies suggests that the implication of CTL escape may be the evolution of HIV to avoid specific responses, and perhaps even the loss of particular MHC/elite control associations. Our group and others have demonstrated that escape mutation containing viruses that are transmitted to individuals without the particular selecting allele can either revert to wild-type sequence or maintain themselves in the new host. The relative frequency of both scenarios must be known to determine if HIV will or will not evolve to evade particular T cell responses, as only the later instance will lead to HIV/SIV evolution. This is nearly impossible in the HIV system, as the sequence of the infecting virus is rarely known. We have systematically mapped both T cell epitopes and T cell escape mutations in SIVmac239 for several common MHC class I alleles in our rhesus macaque system. We are in the process of constructing systematic escape epitope viruses for the A*01, A*02, A*11, B*08 and B*17 class I alleles. We will introduce these viruses into animals that lack the selecting class I alleles and determine the frequency of escape reversion and maintenance. With this knowledge, we will make quantitative conclusions about the implications of CTL escape for various MHC class I alleles, including those associated with elite control. We are presently constructing and testing these viruses in vitro, but intend to complete these studies during the next year. This research used WNPRC Animal Services, Genetics Services, and Immunology &Virology Services. PUBLICATIONS: Valentine LE, Loffredo JT, Bean AT, Le[unreadable]n EJ, MacNair CE, Beal DR, Piaskowski SM, Klimentidis YC, Lank SM, Wiseman RW, Weinfurter JT, May GE, Rakasz EG, Wilson NA, Friedrich TC, O'Connor DH, Allison DB, Watkins DI. Infection with "escaped" virus variants impairs control of simian immunodeficiency virus SIVmac239 replication in Mamu-B*08-positive macaques. J Virol. 2009 Nov;83(22):11514-27. Epub 2009 Sep 2. PMID: 19726517 Loffredo JT, Sidney J, Bean AT, Beal DR, Bardet W, Wahl A, Hawkins OE, Piaskowski S, Wilson NA, Hildebrand WH, Watkins DI, Sette A. Two MHC class I molecules associated with elite control of immunodeficiency virus replication, Mamu-B*08 and HLA-B*2705, bind peptides with sequence similarity. J Immunol. 2009 Jun 15;182(12):7763-75. PMID: 19494300